Chemical Formula: CH3(CH2)16COOH
White or yellowish solid.
Stearic acid is the most common of the long-chain fatty acids.
It is found in many foods, such as beef fat, and cocoa butter.
It is widely used as a lubricant, in soaps, cosmetics, food
packaging, deodorant sticks, toothpastes, and as a softener in rubber.
Stearic acid is a member of the group called fatty acids.
These are hydrocarbon chains (a chain made of repeated units
of a carbon atom and two hydrogen atoms) with a carboxyl
group at one end. A carboxyl group is the COOH in the chemical
formula. It is what turns the hydrocarbon chain into an organic acid.
The carboxyl group in organic acids is reactive, and will easily
lose its hydrogen to a compound that has a hydroxyl group,
which is an oxygen atom joined to a hydrogen atom (OH). The H
from the carboxyl group joins the OH of the hydroxyl group, and
the two become HOH, more commonly seen written as H2O,
or water. The water leaves as a separate molecule, and the
two original molecules become joined at the point where the
carboxyl and hydroxyl groups were.
One compound, glycerol, happens to
have three hydroxyl groups. Glycerol can combine with fatty
acids to form compounds called glycerides.
If there is one fatty acid, you get a mono-glyceride.
If there are two fatty acids, you get a di-glyceride.
When there are three fatty acids, you get a tri-glyceride.
One mono-glyceride is glycerol
stearate. It is glycerol attached to stearic acid.
Because it still has two free hydroxyl groups
attached to the glycerol, that portion of the molecule is
hydrophilic, attracted to water.
The long hydrocarbon chain of the stearic acid
is hydrophobic, attracted to oils and fats instead of water.
This makes it a good emulsifying agent and surfactant.
An emulsifier helps to mix oil and water, to make mixtures
like mayonnaise and butter.
Di-glycerides are also emulsifying agents. You will see
mono- and di-glycerides as ingredients in many foods that
combine oil and water.
Tri-glycerides are fats. The fats in butter, in bacon, and
in your body are all made of tri-glycerides.
Stearic acid is a saturated fatty acid. This means it has only
single bonds between its carbon atoms. This means it can coil up
and form into random shapes. Double bonds between carbon atoms restrict
the bending of the molecule at the point of the bond, like a hinge
that only lets a door swing back and forth, not up and down. Triple
bonds are even more restrictive, locking the joint in place
three-dimensionally, like the legs of a tripod.
Unlike most saturated fats, stearic acid does not seem to increase
cholesterol levels in the blood, because liver enzymes convert it
to an unsaturated fat during digestion.
stearic acid: InChI=1/C18H36O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18(19)20/h2-17H2,1H3,(H,19,20)/f/h19H
By Simon Quellen Field